I've been using metallic / pearlescent prints for years. It's my favorite paper for printing. Here are my observations:
Good for:
1. Any photo that contains a lot of actual metallic subjects (i.e. cars, industrial stuff). The pearlescent layer will make the metal subject appear as if they're made of actual metal. This includes aluminum, steel, silver, bronze, copper, gold, etc.
2. Photos with colors that match certain metals. For example, sunrise/sunset photos can match gold, bronze, and copper. When printed you will get a metallic effect that will be recognized instantly. As a matter of fact, this is my favorite use of metallic prints. I printed this photo: [link] on metallic paper, and it looked like it was etched in copper. I then used a copper-tone frame with a black mat for it. The result was awesome. Unfortunately I had to put glass over it and effect was lessened (see below). Some stone / wood structures have steel / silver feel that I kind of like.
3. You can also get some good effect with green and blue (matching some precious stones), but I'd not get carried away with it.
4. I found that pale and primary yellow juts doesn't work (there really aren't metals or pearls that have that color) and you have to go more orange to get effect of gold.
5. Finally, any color that matches Mother-of-pearl colors (deep violet/blues, dark off-blacks, light pinks, off-whites). They will give effect of being inlaid in Mother-of-Pearl.

Not good for:
1. Portraits. Metallic effect flattens out dimension of a person's face, and the metallic effect just doesn't work on skin tone. Unless there is some robot / iron man cosplay, for example.
2. Photos where shadow detail is very important. Metallic prints don't do as good with shadow detail. Fuji Pearl may be better, see below ...

Now to framing. Framing metallics is extremely difficult. You need good light to enter the paper substrate - that's what makes the print glow and amaze people. Unfortunately if you frame it and put a piece of glass in front of it, unless its some super-optical museum-quality glass, it will steal away some light in form of reflections and will mute the pearlescent effect. I personally would never use glass framing for metallic prints. Instead one method I found was from some company in Berkeley, CA, which mounts a print on a bevel-cut board and sprays the print with UV seal. This will protect the print from damaging sun rays and oddly it actually enhances the pearlescent effect. I have one such print (20x30) mounted this way (it was very expensive actually) but its awesome (I had to ship them the print and they mounted it and shipped back, well over $200 plus shipping).

One last bit. Both Kodak and Fuji make this paper. Kodak calls it Metallic, and Fuji calls it Pearl. Kodak has stronger metallic effect sacrificing some shadow detail in the process, while Fuji has more shadow detail but a slightly weaker effect. I prefer Kodak.

I would suggest getting small prints made by a decent company as samples. Use different subjects and colors and you will see what works and what doesn't.

Hope this helps ...

I have found metalic prints can be very hit and miss. They work EXTREMELY well for some images and very poorly for others. Landscapes generally benefit heavily from it, where as portraits tend to suffer. (Although this is not a hard rule in either case)

There are also metallic toners. The only one I ever tried came out like black chrome on white. Kind of a cool effect, but I just didn't see how it could ever be useful to me.